1. Field of the Invention
This invention relates to improved flame retardant polymer blends comprising a polyalkylene terephthalate resin, an organopolysiloxane-polycarbonate block copolymer and a flame retardant additive. The polymer blends have improved mechanical properties based on impact values and oxygen index values when compared to the same properties associated with polyalkylene terephthalate resins containing a halogenated copolycarbonate flame retardant additive.
2. Description of the Prior Art
LeGrand and Yee recognized--as broadly disclosed in the U.S. patent application Ser. No. 868,023--that blends of certain polyalkylene terephthalate resins and organopolysiloxane-polycarbonate block copolymers have improved mechanical properties including improved heat distortion temperatures and impact values.
Bopp recognized--as disclosed in U.S. patent applications Ser. Nos. 867,985 and 868,021--that blends of polyalkylene terephthalate resins and polysiloxanes have improved mechanical properties including improved heat distortion temperatures, impact and oxygen index values, and unexpectedly--that blends of nonreinforced low molecular weight polyalkylene terephthalate resins and organopolysiloxane-polycarbonate block copolymers have improved mechanical properties including heat distortion temperatures and impact values, respectively.
Although LeGrand et al. and Bopp recognized the improved mechanical properties associated with polyalkylene terephthalate organopolysiloxane-polycarbonate block copolymer blends and polyalkylene terephthalate polysiloxane blends, they did not recognize that blends of polyalkylene terephthalates and organopolysiloxane-polycarbonate block copolymers that contain specific flame retardant additives have still further improved mechanical and chemical properties.